With the progress of computer graphics technology in recent years, data processing devices, such as game devices or simulation devices, have come into wide, general use. Game devices, for example, are provided with peripherals, such as a joystick (operating lever), buttons, a monitor, and the like, a main game device which conducts data communications with these peripherals, as well as image processing, sound processing, and the like, and a display which displays image signals produced by this main device. The image processing in such game devices is of particularly great importance in raising product value, and therefore image reproduction technology has become increasingly refined in recent years.
One known example of a game device of this kind is “Title Fight” (trademark). In this game, the characters (combatants) are composed by sprites (single-layer pictures), and the background and the like is composed by a scrolling screen.
However, by this means, it is not possible to change the viewpoint and represent the characters three-dimensionally. Therefore, in recent years, it has been sought to compose three-dimensional shapes by a plurality of polygons, and to map texture (pattern) onto these polygons and display characters viewed from any viewpoint.
Known examples of this are TV game devices which depict three-dimensional characters by means of texture-mapped polygon data, and depict background sections, where movement is required in accordance with movement of the characters or change in the viewpoint, by means of textured polygon data also, (for example, Sega Enterprises (Co. Ltd.) “Rail Chase I”.)
Thereby, rather than composing characters using sprites, the characters, and the background and the like closely related to the movements of the characters, can be represented as three-dimensional images viewed from prescribed viewpoints.
Incidentally, in a conventional TV game device as described above (for example, Sega Enterprises (Co. Ltd.) “Rail Chase I”), when one stage of the game is completed, the hero characters look at a map and move to the next stage. For this purpose, in this device, the map is formed by separate scroll data, and at the moment one stage has finished, the screen suddenly switches to displaying a map, without any connection to the game environment (First prior art example).
Furthermore, in this device, there is a scene where the hero characters move by riding in a truck, and in this case, the camera work based on the heroes' viewpoint is determined by the direction of movement of the truck. For example, as shown in FIG. 22(a), if the direction changes at points q1, q2, q3, q4, . . . , at point q1, the coordinates of point q2 are read in advance and the viewpoint of the hero characters at point q1 is set in the form of coordinates (X, Y, Z, A) (where A is an angle). In this way, the camera work at the viewpoint of the hero characters as the truck 220 moves to each point q1, q2, q3, q4, is as shown in FIG. 22(b). Specifically, at point q1, for example, it is set as coordinates (X, Y, Z, A) and at point q3, for example, it is set as coordinates (X, Y, Z, B) (where B is an angle).
Here, as shown in FIG. 23, the camera direction is labelled E, the camera orientation is labelled F, and the field of view is labelled G. Thereby, as shown in FIG. 24, before reaching point q11, the camera orientation is F1 and the field of view is G1, after passing point q11 and before reaching point q12, the camera orientation is F2 and the field of view is G2, and after passing point q12 and before reaching point q13, the camera orientation is F3 and the field of view is G3, . . . and in this way, switches in direction occur at individual points, resulting in large changes in the field of view G (Second prior art example).
Moreover, in this device, a river is displayed as a background, or the like. Texture-mapped polygons are used to represent the flow of water in this river, a texture with the appearance of water being applied to the polygons along the flow of the river, and these texture coordinates being changed over time in accordance with the direction of the water flow. For example, as shown in FIG. 25, if texture coordinates are projected onto the polygons 150, 150, . . . about a desired axis, they are displayed such that they move in the same direction as all the polygons 150, 150, . . . . Furthermore, as shown in FIG. 26, if each of the four corners of the polygons 151, 152, 153, 154, 155, 156 is made to correspond to a factor n of the texture, then it is possible to achieve the representation of a winding river flow, according to the shape of each polygon 151, 152, 153, 154, 155, 156 (Third prior art example).
Additionally, in this device, if Z-buffering, which is a technique for erasing hidden surfaces, is used in generating a particular screen, as shown in FIG. 27(a), when looking from viewpoint 210 at a background 220 in the infinite distance, an object in the far distance, or an object 221 having no distance value, the screen has the display range 230 (Fourth prior art example).
Furthermore, since there is a limit on the maximum number of polygons that can be displayed simultaneously using this device, the number of polygons displayed is controlled such that the polygons on the whole screen do not exceed the maximum number (Fifth prior art example).
Incidentally, according to the first prior art described above, there has been a drawback in that the flow of the game is interrupted because a map created separately from the game environment is introduced into the game environment. In other words, there has been a drawback in that, since the viewpoint is usually from within the game, if separate contents are suddenly displayed, this completely disrupts the flow of the game and confuses the player.
Furthermore, according to the second prior art described above, there has been a drawback in that, as shown in FIG. 22 and FIG. 24, at each point q.n (where n is an integer), the camera orientation F is determined by reading the coordinates of the next point, q.n+1, in advance, and hence the viewpoint swings by a large amount because the direction is switched at individual points, and it is hard to create an awareness of the surrounding circumstances. In particular, in curves, dead angles occur more frequently than in reality.
Moreover, according to the third prior art described above, when texture coordinates are projected onto the polygons in the image shown in FIG. 25, the projected surfaces are texture-mapped at a uniform density, but there has been a drawback in that, even if the texture coordinates are moved, they all move in a single direction only, and therefore it is not possible to represent a winding river, for example. Furthermore, in the image shown in FIG. 26, although the texture is made to correspond to the polygons and therefore it can be represented as flowing in a direction corresponding to the shape of the polygons and it can represent the flow of a winding river, there has been a drawback in that the texture density is represented in an altered (compressed) state at changes in the river width, sharp curves, or the like.
In addition, in the fourth prior art described above, three-dimensional computer graphics are used and for this technique, Z-buffering or Z-sorting is often used to display the corresponding image. At present, due to demands for increased speed in processing, in some cases, the Z-buffer (depth information for an object) may be recorded in integer values, or the coordinate values calculated as integers (using a fixed decimal point). Therefore, special processing is conducted if the depth of an object at an infinite distance is to be represented. Moreover, if limits are placed on the display range in the depth direction in order to ensure accuracy when using Z-buffering, then it is necessary to locate the object at a distance that comes within this display range 230. Specifically, as shown in FIG. 27(a), the object 221 must be positioned such that it comes within the display range 230. As a result, there is a drawback in that, if the viewpoint 210 moves towards the left side of the diagram, for example, although the background 220 in the infinite distance moves, the object 221 at a far distance (or an object having no distance value) does not move, and therefore the appearance will change.
Yet further, according to the fifth prior art described above, the total number of polygons on the whole screen is limited. However, there are cases where the game screen is constituted by polygons representing the background and polygons representing enemies, and the like, and in particular, there are cases where the enemies increase in number as the game progresses. Therefore, in order to represent the enemies, the number of polygons for the background is restricted, and in some cases, a part of the background image is lost (so-called polygon error). This loss of the background image causes a marked impairment in the quality of the game image.
In short, there has been the problem that effective image processing cannot be achieved in conventional image processing devices, such as game devices of this type.
Therefore, this invention was made in order to overcome these problems.
A first object of this invention is to provide an image processing device which does not interrupt the flow of a game.
A second object of this invention is to provide an image processing device capable of moving a viewpoint in a natural state.
A third object of this invention is to provide an image processing device capable of displaying natural movement.
A fourth object of this invention is to provide an image processing device comprised such that, even if the viewpoint moves, a screen in the far distance will appear in a similar state to a natural state.
A fifth object of this invention is to provide an image processing device capable of preventing loss of background images.